In a wireless communication device, there is a case where an “adaptive modulation method” which changes a modulation method according to a situation of a radio transmission channel is adopted. In an adaptive modulation method, when a situation of a radio transmission channel is good, a modulation method having a relatively high-speed transmission rate is applied, and when a situation of the radio transmission channel is not good, a modulation method having a relatively low-speed transmission rate is applied, for example. It is possible to change a transmission rate by a multi-value number that is the number of stages for performing modulation and a modulation rate.
In a radio communication system adopting an adaptive modulation method to a wireless communication section, a transmission rate of the wireless communication section varies according to a situation of a radio transmission channel. Because a transmission rate of a wireless communication section corresponds to capacity of information transmission, hereinafter, it is called a bandwidth (transmission capacity).
Meanwhile, in order to deliver time-critical data such as sound and animation to a destination device within a given time on an IP (Internet Protocol) network, a predetermined communication quality is required for the network. In such network, transmission data may be classified into each of its traffic types and the data may be controlled to be forwarded based on priority. Such control is called as service quality (Quality of Service: henceforth, referred to as “QoS”) control. In a communication system in which QoS control is performed, control for guaranteeing a predetermined transmission rate required for transmitting information (henceforth, referred to as “information transmission rate”) is performed. Accordingly, when a bandwidth changes, it is necessary to perform QoS control corresponding to the change. That is, a network environment in which an information transmission rate can be guaranteed even if a bandwidth changes is required.
It is conceivable to apply QoS control used for a wired LAN (Local Area Network) to a radio communication system adopting an adaptive modulation method for a wireless communication section just as it is. In this case, when a bandwidth of a wireless communication section is larger than an information transmission rate, a waiting time until a certain frame is transmitted (henceforth, referred to as a “transmission waiting time”) does not occur. However, when an information transmission rate exceeds a bandwidth of a wireless communication section, there is a possibility that a transmission waiting time occurs, and that so-called “frame loss (packet loss)” that is a case where a frame is discarded without being transmitted occurs.
A technology which performs QoS control in a radio communication system adopting an adaptive modulation method is disclosed in patent document 1, for example. In the technology of patent document 1, presence or absence of QoS control is switched based on a wireless transmission rate. That is, when a wireless transmission rate switches from a high speed to a low speed by a change of a modulation method, QoS control becomes valid. Then, by delaying switching timing of a modulation method, decline of data transfer efficiency by an insufficient wireless transmission rate is suppressed. On the other hand, when a wireless transmission rate switches from a low speed to a high speed by a change in a modulation method, QoS control is canceled.
In an adaptive modulation method, there is also a technology which performs QoS control according to a change in a transmission rate (for example, refer to patent document 2). In the technology of patent document 2, subjects which are operated in order to perform QoS control are a coding rate, a modulation method and a multiplexing scheme or the like.
In an adaptive modulation method, there is also a technology which sets parameters of a modulation method and an equalizer according to priority control by QoS (for example, refer to patent document 3). In the technology of patent document 3, when a high transmission rate is needed, a parameter for a high rate is set, and, when a high rate is not required, a parameter for a low rate is set, for example.